High power fuel cell system

ABSTRACT

A power generator and method include passing ambient air via an ambient air path past a cathode side of the fuel cell to a water exchanger, picking up water from the cathode side of the fuel cell and exhausting air and nitrogen to ambient, passing hydrogen via a recirculating hydrogen path past an anode side the fuel cell to the water exchanger, where the water exchanger transfers water from the ambient air path comprising a cathode stream to the recirculating hydrogen path comprising an anode stream, and passing the water to a hydrogen generator to add hydrogen to the recirculating hydrogen path and passing the hydrogen via the recirculating hydrogen path past the anode side of the fuel cell.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of and claims the benefit ofpriority to U.S. application Ser. No. 15/466,644, filed Mar. 22, 2017,which application is incorporated herein by reference in its entirety.

BACKGROUND

The run time of unmanned air systems (UAS) aka drones is limited bytheir power sources. State of the art UAS use light-weight lithiumion/polymer batteries with specific energies that range from ˜200-300Wh/kg, enabling flight times on the order of 20-60 min. Emergingapplications including infrastructure inspection (e.g. roads, bridges,power lines, rail, pipelines, etc) and package delivery may be desiredto have greater flight times on a battery charge. In some instances,greater than six-hour flight times are desired in order for such as UASto be commercially viable.

The present application is a divisional of and claims the benefit ofpriority to U.S. application Ser. No. 15/466,644, filed Mar. 22, 2017,which application is incorporated herein by reference in its entirety.

Efficient energy storage and utilization faces many obstacles. Protonexchange membrane (PEM) fuel cells for man-portable power and micro airvehicles require light-weight, small-size, and high-rate hydrogensources. Commercially available hydrogen sources such as metal hydrides,compressed hydrogen in cylinders, or catalytic waterborohydride hydrogengenerators are capable of high rate hydrogen generation, but are heavyand bulky.

While some hydrogen generators are light-weight and have small size,they are incapable of generating hydrogen at a sufficiently high ratefor many applications.

SUMMARY

A fuel cell based power generator includes a fuel cell element, a waterexchanger element, a hydrogen generator element, an ambient air pathconfigured to receive ambient air and provide the ambient air across acathode side of the fuel cell element, receive water from the fuel cellelement and provide wet air to the water exchanger element, and arecirculating hydrogen air path configured to receive hydrogen from thehydrogen generator element, provide the hydrogen past an anode side thefuel cell element to the water exchanger element and provide wethydrogen back to the hydrogen generator.

A method include passing ambient air via an ambient air path past acathode side of the fuel cell to a water exchanger, picking up waterfrom the cathode side of the fuel cell and exhausting air and nitrogento ambient, passing hydrogen via a recirculating hydrogen path past ananode side the fuel cell to the water exchanger, where the waterexchanger transfers water from the ambient air path comprising a cathodestream to the recirculating hydrogen path comprising an anode stream,and passing the water to a hydrogen generator to add hydrogen to therecirculating hydrogen path and passing the hydrogen via therecirculating hydrogen path past the anode side of the fuel cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a power generator having arecirculating hydrogen path past a fuel cell and hydrogen generatoraccording to an example embodiment.

FIG. 2 is a conceptual cross section of a power generator utilizing therecirculating hydrogen path according to an example embodiment.

FIG. 3 is a perspective view of a water exchanger for power generatorillustrating example water exchanger operating principles according toan example embodiment.

FIG. 4 is perspective cut-away view of an example water exchangeraccording to an example embodiment.

FIG. 5 is a perspective view of an unmanned air system (UAS) utilizingthe power generator according to example embodiments.

FIG. 6 is a chart illustrating fuel cell based power generatorperformance compared to an Li-Ion battery according to an exampleembodiment.

FIG. 7 is chart illustrating fuel cell based power generator specificenergy decrease during discharge due to oxygen accumulation in reactionproducts according to an example embodiment.

FIG. 8 is chart illustrating energy density differences between twoalternative kWh fuel cell designs and a Li-Ion battery according toexample embodiments.

FIG. 9 is a chart illustrating characteristics of the two fuel celldesigns of FIG. 9

FIG. 10 is a perspective view of a UAS illustrating an open batterycompartment according to an example embodiment.

FIG. 11 is a block cross section diagram illustrating selected layers ofa fuel cell stack is a cross section diagram of a hydrogen fuel cellbased power generator according to an example embodiment.

FIG. 12 is a flowchart illustrating a method of controlling thetemperature of multiple elements of a fuel cell based power generatoraccording to an example embodiment.

FIG. 13 is a block diagram of a specifically programmed circuitry orprocessor for executing control methods for a hydrogen fuel cell basedpower generator according to an example embodiment.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings that form a part hereof, and in which is shown by way ofillustration specific embodiments which may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatother embodiments may be utilized and that structural, logical andelectrical changes may be made without departing from the scope of thepresent invention. The following description of example embodiments is,therefore, not to be taken in a limited sense, and the scope of thepresent invention is defined by the appended claims.

The functions or algorithms described herein may be implemented insoftware in one embodiment. The software may consist of computerexecutable instructions stored on computer readable media or computerreadable storage device such as one or more non-transitory memories orother type of hardware based storage devices, either local or networked.Further, such functions correspond to modules, which may be software,hardware, firmware or any combination thereof. Multiple functions may beperformed in one or more modules as desired, and the embodimentsdescribed are merely examples. The software may be executed on a digitalsignal processor, ASIC, microprocessor, or other type of processoroperating on a computer system, such as a personal computer, server orother computer system, turning such computer system into a specificallyprogrammed machine.

The run time of unmanned air systems (UAS) aka drones is limited bytheir power sources. State of the art UAS use light-weight lithiumion/polymer batteries with specific energies that range from ˜200-300Wh/kg, enabling flight times on the order of 20-60 min. Emergingapplications including infrastructure inspection (e.g. roads, bridges,power lines, rail, pipelines, etc) and package delivery require longerflight times in order to be commercially viable. In various embodiments,a high specific energy power source including a fuel cell may be usedfor battery powered devices, such as a UAS, capable of providing 10-12×the run time of state of the art lithium batteries. Some embodiments mayprovide six to twelve or more hours of flight time.

A hybrid fuel cell power generator provides run time improvement andenergy efficiency under specified load power profiles. Moreover, thehybrid fuel cell power generator may be substantially lighter than priorenergy storage devices and may have lower projected lifecycle costs,without compromising operation temperature range or environmental andsafety performance. A revolutionary improvement in runtime lies in theinnovative fuel-cell technology and its fuel chemistry based on lithiumaluminum hydride (LAH) that requires no net water consumption in orderto sustain its operation, thus eliminating the need for a water fuelreservoir, which enables the energy source to be substantially smallerand lighter than other conventional chemical hydride or direct methanolfuel cells with on-board storage of water (fuel, diluent, or solvent).

A fuel cell based power generator is illustrated at 100 in schematicform in FIG. 1. In one embodiment power generator 100 includes a fuelcell 110 and a hydrogen generator 115. An ambient air path 120 isconfigured to run ambient air past a cathode side of the fuel cell 110.A reaction in the fuel cell 110 adds water to the ambient air path 120,providing it to the hydrogen generator 115, which contains one or morefuels that release hydrogen responsive to exposure to water, which maybe in the form of humidity. The hydrogen generator 115 provides thereleased hydrogen to a recirculating hydrogen path 125, which runs pastthe anode side of the fuel cell 110 to provide the hydrogen. Hydrogenfrom the recirculating hydrogen path 125 reacts with oxygen from theambient air path 120 in fuel cell 110, producing water vapor and heat asreactions byproducts, which is removed from the fuel cell by the airflowing within ambient airflow path 120. Nitrogen and leftover hydrogencontinues on through the recirculating hydrogen path 120.

In one embodiment, electricity generated by the fuel cell 110 isprovided for storage in one or more batteries, such as li-ionrechargeable batteries. Power management circuitry 135 may utilize theultra-high-power rechargeable battery 120, such as a Li-ion batterymanufactured by Saft America Inc., that is capable of handling variousload power profiles with significant transient fluctuations. Otherrechargeable batteries may be used in further embodiments.

In one embodiment, the fuel cell based power generator 100 has a systemconfiguration (implemented in a X590 form factor battery package in oneembodiment) and operating principle are schematically depicted inFIG. 1. Hydrogen generator 115 in one embodiment is a replaceable anddisposable “fuel-cartridge” unit that generates H₂ for a H₂/oxygenproton exchange membrane (PEM) fuel cell 110, and a permanent unit thatin one embodiment includes (PEM) fuel cell 110, Li-ion recharge battery130 as an output stage to interface with an external load, and the powermanagement module 135 that controls electronic and fluidic controlcircuits (controlling multiple fans) to dynamically sense and optimizethe power generator 100 under varying load and environmental conditions.

The fuel cell based power generator 100 in various embodiment mayinclude one or more of the following innovative aspects:

-   Hybridization between a fuel cell and Li-ion rechargeable batteries    maximizes total energy and extraction efficiency to meet load power    profiles with transients-   Ultra high power lithium-ion rechargeable batteries enabling high    power management efficiency-   Water-less fuel cell operation scavenges water in vapor from its    cathode and uses it as fuel in the H2 generation process, enabling    longer runtime and lighter weight than a BA5590 lithium battery:-   High fuel energy density (>3100 Whr/liter) and specific energy    (>3300 Whr/kg)-   Broad environmental operating and storage range-   LAH-based fuel chemistry (water-vapor driven reaction), and    engineered fuel formulation (particle size and porosity)    enabling >95% fuel utilization at high power-   Replaceable and disposable fuel-cartridge configuration enabling    further enhanced runtime and weight advantages for extended mission    duration and reduced life-cycle cost-   Hot-swappable fuel cartridges for uninterrupted power

Ambient air serves as the hybrid fuel cell power generator 100 oxygensource, carrier gas for the water vapor fuel, and coolant gas for thefuel cell stack and H₂ generator. A first fan 140 draws in fresh airfrom ambient via an inlet 142, circulates it over the cathode side ofthe fuel cell stack via an ambient air path or passage 120. Since thefuel cell 110 reaction is exothermic, the temperature of the fuel cell110 increases as may be measured by a first temperature sensorrepresented at 144, which is positioned to measure the temperature ofthe fuel cell 110. A fuel cell set point temperature of the fuel cell110 is indicated as 60° C., which has been found to be a temperature atwhich the fuel cell 110 functions most efficiently due to increasedproton conductivity. In further embodiments, the set point may varybetween 60° C. and 80° C., and may vary further depending on theconfiguration and specific materials. Different optimal set points forthe fuel cell may be determined experimentally for different fuel cellsand may be found to be outside the range specified above. The controlelectronics 135 may use PID type control algorithms to control the firstfan 140 speed to maintain the fuel cell temperature at its set point.Other control algorithms may be used in further embodiments, suchmodeling and any other type of algorithm sufficient to control thetemperature to the set point by controlling the first fan 140 speed.

The ambient air path 120 continues through a first heat exchanger 145with a second fan 150, and then through water exchanger 155. The waterexchanger 155 operates optimally at a water exchanger set pointtemperature as indicated at 157, which also represents a temperaturesensor configured to sense the temperature of the water exchanger 157.The water exchanger 157 extracts water from warm wet air exiting theheat exchanger 145, and exhausts hot, dry exhaust to ambient at 160. Thefan 150 of heat exchanger 145 may be controlled in the same manner asfan 140 to maintain the flow of warm wet air to the water exchanger 155to maintain the water exchanger 157 at its set point temperature, whichin one embodiment is 40° C. and may vary from 40° C. to 60° C. in someembodiments, or outside that range depending on the type of waterexchanger utilized.

The hydrogen generator 115 also has a set point temperature at which itoperates most efficiently as represented at 163, which also represents asuitably positioned temperature sensor. The hydrogen generatorexperiences an exothermic reaction and has an optimal operating setpoint is shown as 80° C., but may vary from 60° C.-100° C. or outsidethe range depending on the composition of the hydrogen generator used.The hydrogen generator temperature may be controlled by varying a speedof a hydrogen path fan or pump 165 via the control electronics 135 in asimilar manner as that used for the other fans, such as PID type controlalgorithms. Faster operation of the various fans generally lowers thetemperature of the corresponding element.

The hydrogen path 125 does not dead-end at the fuel cell as that canresult in the accumulation of reaction byproducts, such as nitrogenbuilding in the fuel cell resulting in hydrogen starvation in the fuelcell and decreased performance Rather, the hydrogen path 125 continuespast the fuel cell, preventing build-up of nitrogen and providing acontinuous flow of hydrogen to the fuel cell. The hydrogen path 125carries hot, dry H₂ to a hydrogen path heat exchanger 170 having a fan175 controlled by the control electronics to reduce the temperature ofthe hot, dry H₂ to warm dry H₂ provided to the water exchanger 155 basedon temperature sensor 157. In some embodiments, heat exchanger 170 maybe positioned in the flow path between the hydrogen generator and fuelcell, to better optimize the temperature of the fuel cell. In furtherembodiments, the temperature sensor 157 may comprise multiple differenttemperature sensors measuring the temperature in both ambient andhydrogen paths between the heat exchangers 145 and 170 and the waterexchanger 157. Such different temperature sensors may be used to eitherindependently control fans 150 and 175 to provide their exhausts attemperatures suitable for the set point of the water exchanger. Infurther embodiments, the control of the heat exchanger fans may beinterdependent to maintain the water exchanger at the desired set point.The water exchanger 155 thus receives warm wet air from the ambientpath, and warm dry H₂ from the recirculating hydrogen path, and provideswet H₂ to the hydrogen generator, while exhausting hot, dry exhaustwhich may include nitrogen, to ambient.

Three elements are shown as having different set points at which theyoperate most efficiently, the water exchanger 155, the hydrogengenerator 115, and the fuel cell 110. Each is shown as having adifferent set point with temperature controlled by fan speed. Thecontrol may be independent for each element, or in some embodiments thatmay utilize a model based control algorithm, the control may be providedinterdependently based on the model.

In a further embodiment, one or more of the elements whose temperatureis controlled may include a heater, such as a resistive heater poweredby the battery to initially heat the element when the PEM fuel cellbased generator is being started. While the elements will reachoperating ranges without addition heaters, the heaters can assist theelement or elements to reach an optimal operation temperature morequickly, enabling a power device to operate at full power more quickly.

In one embodiment, as gases passes by the fuel cell stack from theambient path 120 and the recirculating hydrogen path 125, oxygen isconsumed by the fuel cell, and water vapor and waste heat are absorbed.Nitrogen is included with the hot, dry H₂ in the hydrogen path 125, andwater vapor and air in the ambient path 120.

As the air passes through the H₂ generator, it also absorbs waste heatfrom the fuel. The electrical power generated in the fuel cell stack maybe fed to power management circuitry 135 which conditions the power andprovides it to a load as indicated by contacts 180. A suite of sensorsmay measure, in addition to the temperature sensor previously described,humidity, and pressure throughout the system 100. Data provided by thesensors, as well as the electrical load and charge state of the Li-ionrechargeable batteries 120 are used by the control electronics 135 todetermine and set the various fan speeds to control the temperature ofthe elements to corresponding set points.

Fuel consumption may also be monitored, and the remaining capacity maybe displayed on the hybrid fuel cell power generator packaging invarious embodiments. In one embodiment, greater than 95% fuelutilization may be achieved through optimized LAH fuel formation(porosity, particle size/distribution, rate enhancing additives).

In some embodiments, the LAH-water reaction generates a substantialamount of heat (150 kJ/mol LAH, exothermic) leading to a rise intemperature in the fuel. The temperature may be monitored along withcontrolling airflow over the stack to maintain temp at a desired setpoint for optimal operation.

Electrochemical system power performance can substantially degrade atlow temperatures (−40° C.) due to slower reaction kinetics and lowerelectrolyte conductivity. The hybrid fuel cell may avoid freezingproblems by 1) using water in vapor form, 2) adjusting airflow toprevent water vapor condensation, and 3) using heat generated by thefuel cell stack and H2 generator to regulate the temperature of the fuelcell stack and fuel rods.

In some embodiments, noryl plastic packaging consistent with the typeused on the Saft BA5590 may be used. Many different types of plasticsand other materials that provide low weight yet sufficient tolerance tothe operating parameters and environmental conditions of the generatormay be used.

Hydrogen generator 115 in one embodiment is a high-rate hydrogengenerator suitable for man-portable power and micro air vehicleapplications that provides 4-5× the hydrogen of commercially availablehydrogen sources of the same size and weight. Many different hydrogenproducing fuels, such as LAH may be used. In further embodiments, thehydrogen producing fuel may include LiAlH₄, NaAlH₄, KAlH₄, MgAlH₄, CaH₂,LiBH₄, NaBH₄, LiH, MgH₂, Li₃Al₂, CaAl₂H₈, Mg₂Al₃, alkali metals,alkaline earth metals, alkali metal silicides, or any combinationsthereof.

The term “about” as used herein can allow for a degree of variability ina value or range, for example, within 10%, within 5%, or within 1% of astated value or of a stated limit of a range, and includes the exactstated value or range.

The term “substantially” as used herein refers to a majority of, ormostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%,98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more, or100%.

Hydrogen-Generating Composition for a Fuel Cell.

In various embodiments, the present invention provides ahydrogen-generating composition for a fuel cell. The hydrogen-generatingcomposition can include a hydride and a Lewis acid. Thehydrogen-generating composition can be combined with water to generatehydrogen gas. The phase of the water contacted with thehydrogen-generating composition to generate the hydrogen gas can be anysuitable phase, such as liquid water (e.g., in a pure state, dilutedstate, or such as having one or more compounds or solvents dissolvedtherein) or gaseous water (e.g., water vapor, at any suitableconcentration). The generated hydrogen gas can be used as the fuel for ahydrogen-consuming fuel cell.

The hydrogen-generating composition can be in any suitable form. Thehydrogen-generating composition can be in the form of a loose powder, ora compressed powder. The hydrogen-generating composition can be in theform of grains or pellets (e.g., a powder or grains compressed intopellets). The hydrogen-generating composition can have any suitabledensity, such as about 0.5 g/cm³ to about 1.5 g/cm³, or about 0.5 g/cm³or less, or less than, equal to, or greater than about 0.6 g/cm³, 0.7,0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4 g/cm³, or about 1.5 g/cm³ or more.

In some embodiments, when contacted with water the hydrogen-generatingcomposition forms fewer (e.g., a smaller mass per mass of hydrogenformed) non-hydrogen materials as compared to a correspondinghydrogen-generating composition including less or none of the Lewisacid. The non-hydrogen materials that are formed less or not at allduring hydrogen production can be hydrates (e.g., hydrated hydroxides)of the hydride in the hydrogen-generating composition. By avoidingproduction of unwanted (e.g., non-hydrogen) materials during hydrogengeneration, the amount of hydrogen that can be produced per mass of thehydrogen-generating composition can be greater than that of acorresponding hydrogen-generating composition including less or none ofthe Lewis acid or less or none of the metal oxide.

In some embodiments, when contacted with water the hydrogen-generatingcomposition forms hydrogen gas at a higher rate as compared to acorresponding hydrogen-generating composition including less or none ofthe Lewis acid. For example, a given mass of the hydrogen-generatingcomposition can form a given number of moles of hydrogen gas in lesstime when contacted with a given mass of water as compared to the amountof time required for the same mass of a correspondinghydrogen-generating composition, including less or none or the Lewisacid or including less or none of the metal oxide, contacted with thesame mass of water to produce the same number of moles of hydrogen gas.The rate of hydrogen generation of embodiments of thehydrogen-generating composition can exceed the rate of a correspondinghydrogen-generating composition including less or none or the Lewis acidor including less or none of the metal oxide by any suitable amount; forexample, the rate can be greater than 1 times greater to equal to orless than about 20 times greater as compared to a correspondinghydrogen-generating composition including less or none of the Lewisacid, or about 2.5 to about 7.5 times greater, or about 2 times greateror less, or less than, equal to, or greater than about 2.5 timesgreater, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 9, 10, 11, 12, 13,14, 15, 16, 18, or about 20 or more times greater.

In some embodiments, the hydrogen-generating composition issubstantially free of elemental metals. In some embodiments, thehydrogen-generating composition can be substantially free of elementalaluminum.

Hydride.

The hydrogen-generating composition may include one or more hydrides.The one or more hydrides can form any suitable proportion of thehydrogen-generating composition, such as about 50 wt % to about 99.999wt %, about 70 wt % to about 99.9 wt %, about 70 wt % to about 90 wt %,or about 50 wt % or less, or less than, equal to, or greater than about52 wt %, 54, 56, 58, 60, 62, 64, 66, 68, 70, 71, 72, 73, 74, 75, 76, 77,78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 92, 94, 96, 98, 99,99.9, 99.99, or about 99.999 wt % or more.

The hydride can be any suitable hydride, such that thehydrogen-generating composition can be used as described herein. Thehydride can be a compound in which one or more hydrogen centers (e.g.,one or more hydrogen atoms, or a group that includes one or morehydrogen atoms) having nucleophilic, reducing, or basic properties. Thehydrogen atom in the hydride can be bonded to a more electropositiveelement or group. For example, the hydrogen can be chosen from an ionichydride (e.g., a hydrogen atom bound to an electropositive metal, suchas an alkali metal or alkaline earth metal), a covalent hydride (e.g.,compounds including covalently bonded hydrogen and that react ashydride, such that the hydrogen atom or hydrogen center has nucleophilicproperties, reducing properties, basic properties, or a combinationthereof), a metallic hydride (e.g., interstitial hydrides that existwithin metals or alloys), a transition metal hydride complex (e.g.,including compounds that can be classified as covalent hydrides orinterstitial hydrides, such as including a single bond between thehydrogen atom and a transition metal), or a combination thereof.

The hydride can be chosen from magnesium hydride (MgH₂), lithium hydride(LiH), aluminum hydride (AlH₃), calcium hydride (CaH₂), sodium aluminumhydride (NaAlH₄), sodium borohydride (NaBH₄), lithium aluminum hydride(LiAlH₄), ammonia borane (H₃NBH₃), diborane (B₂H₆), palladium hydride,LaNi₅H₆, TiFeH₂, and a combination thereof. The hydride can be chosenfrom lithium aluminum hydride (LiAlH₄), calcium hydride (CaH₂), sodiumaluminum hydride (NaAlH₄), aluminum hydride (AlH₃), and a combinationthereof. The hydride can be lithium aluminum hydride (LiAlH₄).

In some embodiments, the hydrogen-generating composition only includes asingle hydride and is substantially free of other hydrides. In someembodiments, the hydrogen-generating composition only includes one ormore hydrides chosen from lithium aluminum hydride (LiAlH₄), calciumhydride (CaH₂), sodium aluminum hydride (NaAlH₄), and aluminum hydride(AlH₃), and is substantially free of other hydrides. In someembodiments, the hydrogen-generating composition only includes thehydride lithium aluminum hydride (LiAlH₄), and is substantially free ofother hydrides. In some embodiments, the hydrogen-generating compositioncan be substantially free of simple hydrides that are a metal atomdirectly bound to a hydrogen atom. In some embodiments, thehydrogen-generating composition can be substantially free of lithiumhydride and beryllium hydride.

In some embodiments, the hydrogen-generating composition can besubstantially free of hydrides of aluminum (Al), arsenic (As), boron(B), barium (Ba), beryllium (Be), calcium (Ca), cadmium (Cd), cerium(Ce), cesium (Cs), copper (Cu), europium (Eu), iron (Fe), gallium (Ga),gadolinium (Gd), germanium (Ge), hafnium (Hf), mercury (Hg), indium(In), potassium (K), lanthanum (La), lithium (Li), magnesium (Mg),manganese (Mn), sodium (Na), neodymium (Nd), nickel (Ni), lead (Pb),praseodymium (Pr), rubidium (Rb), antimony (Sb), scandium (Sc), selenium(Se), silicon (Si), samarium (Sm), tin (Sn), strontium (Sr), thorium(Th), titanium (Ti), thallium (Tl), vanadium (V), tungsten (W), yttrium(Y), ytterbium (Yb), zinc (Zn), zirconium (Zr), hydrides of organiccations including (CH₃) methyl groups, or a combination thereof. Invarious embodiments, the hydrogen-generating composition can besubstantially free of one or more of lithium hydride (LiH), sodiumhydride (NaH), potassium hydride (KH), magnesium hydride (MgH₂), calciumhydride (CaH₂), lithium aluminum hydride (LiAlH₄), sodium borohydride(NaBH₄), lithium borohydride (LiBH₄), magnesium borohydride Mg(BH₄)₂,sodium aluminum hydride (NaAlH₄), or mixtures thereof.

In some embodiments, the hydrogen-generating composition includes ametal hydride (e.g., an interstitial intermetallic hydride). Metalhydrides can reversibly absorb hydrogen into their metal lattice. Themetal hydride can be any suitable metal hydride. The metal hydride canbe LaNi₅, LaNi_(4.6)Mn_(0.4), MnNi_(3.5)Co_(0.7)Al_(0.8),MnNi_(4.2)Co_(0.2)Mn_(0.3)Al_(0.3), TiFe_(0.8)Ni_(0.2), CaNi₅,(V_(0.9)Ti_(0.1))_(0.95)Fe_(0.05), (V_(0.9)Ti_(0.1))_(0.95)Fe_(0.05),LaNi_(4.7)Al_(0.3), LaNi_(5-x)Al_(x) wherein x is about 0 to about 1, orany combination thereof. The metal hydride can be LaNi_(5-x)Al_(x)wherein x is about 0 to about 1 (e.g., from LaNi₅ to LaNi₄Al). The metalhydride can form any suitable proportion of the hydrogen-generatingcomposition, such as about 10 wt % to about 99.999 wt %, or about 20 wt% to about 99.5 wt %, or about 10 wt % or less, or less than, equal to,or greater than about 15 wt %, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29,30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 91, 92, 93, 94, 95,96, 97, 98, 99, 99.5, 99.9, 99.99, or about 99.999 wt % or more. Anymetal hydride that is described in U.S. Pat. No. 8,172,928, incorporatedby reference herein in its entirety, can be included in the presenthydrogen-generating composition.

The hydrogen-generating composition can include both a metal hydride(e.g., an interstitial intermetallic hydride, such as LaNi_(5-x)Al_(x)wherein x is about 0 to about 1), and a chemical hydride (e.g., an ionichydride or a covalent hydride, such as magnesium hydride (MgH₂), lithiumhydride (LiH), aluminum hydride (AlH₃), calcium hydride (CaH₂), sodiumaluminum hydride (NaAlH₄), sodium borohydride (NaBH₄), lithium aluminumhydride (LiAlH₄), ammonia borane (H₃NBH₃), diborane (B₂H₆), palladiumhydride, LaNi₅H₆, TiFeH₂, and a combination thereof). In someembodiments, the hydrogen-generating composition can include a uniformblend of the chemical hydride, the metal hydride, and the Lewis acid. Insome embodiments, the hydrogen-generating composition can include themetal hydride separate from a mixture of the chemical hydride and theLewis acid, such as a fuel pellet including a metal hydride and adifferent fuel pellet including an intimate mixture of a chemicalhydride and a Lewis acid.

A hydrogen-generating composition including a chemical hydride, a metalhydride, and a Lewis acid can include any suitable proportion of thechemical hydride, such as about 0.5 wt % to about 65 wt %, or about 0.5wt % or less, or less than, equal to, or greater than about 1 wt %, 2,3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, or about 65 wt % ormore. A hydrogen-generating composition including a chemical hydride, ametal hydride, and a Lewis acid can include any suitable proportion ofthe metal hydride, such as about 20 wt % to about 99.5 wt %, or about 20wt % or less, or less than, equal to, or greater than about 25 wt %, 30,35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, orabout 99.5 wt % or more. A hydrogen-generating composition including achemical hydride, a metal hydride, and a Lewis acid can include anysuitable proportion of the Lewis acid, such as about 0.1 wt % to about20 wt %, or about 0.1 wt % or less, or less than, equal to, or greaterthan about 0.5 wt %, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, or about20 wt % or more. In one example, a hydrogen-generating compositionincludes 5 vol % LaNi_(5-x)Al_(x) wherein x is about 0 to about 1, andis about 60.9 wt % LaAlH₄, about 15.2 wt % ZrCl₄, and about 23.8 wt %LaNi_(5-x)Al_(x). In another example, the hydrogen-generatingcomposition includes 95 vol % LaNi_(5-x)Al_(x) wherein x is about 0 toabout 1, and is about 0.7 wt % LiAlH₄, about 0.2 wt % ZrCl₄, and about99.1 wt % LaNi_(5-x)Al_(x).

Lewis Acid.

The hydrogen-generating composition includes one or more Lewis acids.The one or more Lewis acids can form any suitable proportion of thehydrogen-generating composition, such as about 0.001 wt % to about 50 wt% of the hydrogen-generating composition, about 0.1 wt % to about 30 wt%, about 10 wt % to about 30 wt %, about 0.001 wt % or less, or lessthan, equal to, or greater than about 0.01 wt %, 0.1, 1, 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,26, 27, 28, 29, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, or about 50 wt %or more.

The Lewis acid can be any suitable Lewis acid, such that thehydrogen-generating composition can be used as described herein. TheLewis acid can be an inorganic compound or an organometallic compound inwhich a cation of the Lewis acid is selected from the group consistingof scandium, titanium, vanadium, chromium, manganese, iron, cobalt,copper, zinc, boron, aluminum, yttrium, zirconium, niobium, molybdenum,cadmium, rhenium, lanthanum, erbium, ytterbium, samarium, tantalum, andtin. The anion of the Lewis acid can be a halide. The Lewis acid can bechosen from aluminum chloride (AlCl₃), aluminum bromide (AlBr₃),aluminum fluoride (AlF₃), stannous (II) chloride (SnCl₂), stannous (II)bromide (SnBr₂), stannous (II) fluoride (SnF₂), magnesium chloride(MgCl₂), magnesium bromide (MgBr₂), magnesium fluoride (MgF₂), zirconium(IV) chloride (ZrCl₄), zirconium (IV) bromide (ZrBr₄), zirconium (IV)fluoride (ZrF₄), tungsten (VI) chloride (WCl₆), tungsten (VI) bromide(WBr₆), tungsten (VI) fluoride (WF₆), zinc chloride (ZnCl₂), zincbromide (ZnBr₂), zinc fluoride (ZnF₂), ferric (III) chloride (FeCl₃),ferric (III) bromide (FeBr₃), ferric (III) fluoride (FeF₃), vanadium(III) chloride, vanadium (III) bromide, vanadium (III) fluoride, and acombination thereof. The Lewis acid can be chosen from aluminum chloride(AlCl₃), magnesium chloride (MgCl₂), zirconium (IV) chloride (ZrCl₄),and a combination thereof. The Lewis acid can be zirconium (IV) chloride(ZrCl₄).

Metal Oxide.

In various embodiments, the hydrogen-generating composition can includeone or more metal oxides. In some embodiments, the hydrogen-generatingcomposition can be free of metal oxides. The one or more metal oxidescan form any suitable proportion of the hydrogen-generating composition,such as about 0.001 wt % to about 20 wt % of the hydrogen-generatingcomposition, about 1 wt % to about 10 wt %, or about 0.001 wt % or less,or less than, equal to, or greater than about 0.01, 0.1, 1, 2, 3, 4, 5,6, 7, 8, 9, 10, 12, 14, 16, 18, or about 20 wt % or more.

The metal oxide can be any suitable metal oxide, such that thehydrogen-generating composition can be used as described herein. Themetal oxide can be zirconium (IV) oxide, hafnium (IV) oxide, titanium(IV) oxide, or a combination thereof. The metal oxide can be titanium(IV) oxide.

The hydrogen-consuming fuel cell can include an anode, a cathode, and anelectrically-insulating ion-conducting electrolyte (e.g., a membrane,such as a proton exchange membrane, or PEM) separating the anode andcathode, wherein at least one of the anode or cathode undergoes achemical reaction that consumes hydrogen and generates an electricalpotential across the electrodes. In some embodiments, the cathode of thefuel cell consumes hydrogen gas and generates electrons and hydrogenions. The hydrogen ions can travel across the electrolyte to thecathode, while the electrons can travel to the cathode via an electricalcircuit connecting the anode to the cathode. At the cathode, thehydrogen ions can react with oxygen gas and the electrons produced bythe anode to form water.

The water vapor reacts with the chemical hydride fuel in the hydrogengenerator, and generates hydrogen in an exothermic reaction. Thehydrogen is carried to a PEM fuel cell as illustrated in FIG. 1 togenerate electrical power. Rather than deadending the hydrogen path, thehydrogen path continues along the PEM fuel cell and recirculateshydrogen back through the hydrogen generator. The hydrogen generator 100interfaces with a fuel cell system, and may be contained in areplaceable and disposable (recyclable) cartridge such as a container.These cartridges may provide a low-cost source of energy having adramatic improvement in energy versus prior batteries and fuel cellsystems in part, because the fuel cell system is retained, while onlythe cartridge is replaced. The power generator 100 may be cylindrical ingeometry in one embodiment.

FIG. 2 is a conceptual cross section of a power generator 200 utilizinga PEM 205 and a recirculating hydrogen path 210 as previouslyillustrated in schematic form in FIG. 1. The hydrogen fuel includes botha metal hydride, LaNiAl as indicated at 215, and a chemical hydride,LiAlH₄ as indicated at 220. The fuel may include one or more differenthydrogen producing fuels as described above.

Circulation fans are shown at 225 and are used to control thetemperature of various elements to corresponding element set points. Anambient airpath is shown at 230. A cooling fan is shown at 240 at thebottom of the generator 200. A fuel cell and water recovery membrane iswrapped around a perimeter of the power generator, which may be in theform of a cartridge in some embodiments. In one embodiment, a fuelcell/water recovery membrane 245 is wrapped around a perimeter of thefuel cartridge. A fan in the ambient airpath 230 transfers water to thewater recovery membrane and also cools the fuel. A fan in the hydrogenpath provides hydrogen to the fuel cell, transfers water from the waterrecovery membrane to the fuel and cools the fuel. These fans are shownin FIG. 1. Cooling fan 240 on the bottom of the fuel cartridge may alsocontrol the temperature of the hydrogen generator.

In various embodiments, the fuel cell based power generator mayimplemented in various micro fuel cell form factors with improvedperformance vs. lithium batteries that may be 3-5× smaller, 5-10×lighter, and highly scalable form factor, energy, and electricalcharacteristics. Fuel cell performance advantages may scale to kW powerlevels, ideal for UAS, UGV, UUV applications. In one embodiment, the useof a fuel cell based power generator may enables 8-12 hr flight times ina UAS vs. 50 minutes for Li-ion, which may be 10-12× longer than Li-ionbatteries, resulting in a virtually silent, long endurance ISR platformwith outstanding capability and stability

FIG. 3 is a perspective view of a water exchanger 300 for powergenerator illustrating example water exchanger operating principlesaccording to an example embodiment. The water exchanger consists of anumber of tubes or channels 310 with flow in one direction adjacentchannels 315 with flow in an opposite direction. The channels may beformed as layers with walls that stack and allow transfer of water vaporbetween them. Water molecules may be absorbed into walls of Nafion®tubes and transferred to a dry gas steam. The transfer process may bedriven by a difference in partial pressure of water vapor on opposingsides.

FIG. 4 is perspective cut-away view of an example water exchanger 400according to an example embodiment. Water exchanger 400 is illustratedwith a dry hydrogen inlet 410 and wet hydrogen outlet 420, correspondingto the anode stream, and humid air inlet 415 and dry air outlet 425,corresponding to the cathode stream. Water is transferred from thecathode stream to the anode stream in the water exchanger. In oneembodiment, an FC™—series humidifier may be used for water exchanger155.

FIG. 5 is a perspective view of an unmanned air system (UAS) 500utilizing the power generator according to example embodiments. The fuelcell based power generator may be adapted to fulfill publishedrequirements for long endurance VTOL ISR system operation. Two exampledesign points include projected fuel cell performance for two designs:1200 W power, 8 kWh energy and 1200 W power, 12 kWh energy.

FIG. 6 is a chart illustrating fuel cell based power generatorperformance at 600 compared to an Li-Ion battery according to an exampleembodiment. Fuel cell performance compares favorably to Li-ion,providing 8-12 hrs of projected runtime in a UAS, vs. ˜50 minutes forLi-ion. Fuel cell provides ˜10-12× the flight time of Li-ion.

FIG. 7 is chart 700 illustrating fuel cell based power generatorspecific energy decrease during discharge due to oxygen accumulation inreaction products according to an example embodiment. Fuel cell specificenergy decreases during discharge due to oxygen accumulation in reactionproducts. Initial (beginning of life) values range from ˜2500-3000Wh/kg, for the two designs. Final (end of life) values range from˜1500-1650 Whr/kg, for the two designs. Battery specific energy constantat ˜220 Wh/kg. Fuel cell variable mass (and resulting power consumption)is accounted for in analysis.

FIG. 8 is chart 800 illustrating energy density differences between twoalternative kWh fuel cell designs and a Li-Ion battery according toexample embodiments.

FIG. 9 is a chart 900 illustrating characteristics of the two fuel celldesigns of FIG. 8.

Fuel cell energy density ranges from 1400-1800 Wh/L for the two designs,compared to ˜300 Wh/L for Li-ion. Fuel cell energy density may be 4-6×Li-ion.

FIG. 10 is a perspective view of a UAS 1000 illustrating an open batterycompartment 1010 according to an example embodiment. A hinged cover 1015is show open. In one embodiment, the compartment 1010 provides space andcooling for fuel cell integration. The fuel cell based power generatorwill provide power resulting in a virtually silent long endurance ISRplatform with outstanding capability and stability. The use of thehybrid power generator with batteries charged from the fuel cell willprovide rates of electrical power suitable for the above functions.Multiple functions combined with long endurance provides maximumoperational value and flexibility.

FIG. 11 is a block cross section diagram illustrating selected layers ofan example fuel cell stack. Note that this is just one example of a fuelcell stack and that other fuel cell stacks may be utilized in furtherembodiments. Starting to the top of the selected layers and oxygen flowchannel 1110 is shown. A cathode electrode 1115 is adjacent the flowchannel 1110, followed by a gas diffusion layer 1120 adapted tocorrespond to each of the cells, with an adhesive layer 1130. A membraneelectrode assembly layer 1140 is then disposed to receive oxygen fromthe flow channel 1110, which is porous, and through the gas diffusionlayer 1130 on a first side. Hydrogen from a hydrogen flow channel 1145on the other side of the membrane electrode assembly layer 1140 passesthrough an anode electrode layer 1145, and gas diffusion layer 1150adhered between the membrane electrode assembly layer 1140 and gasdiffusion layer 1150 by an adhesive layer 1155. The hydrogen and oxygenreact at the membrane electrode assembly layer 1140 to produceelectricity, which is conducted by the anode and cathode electrodelayers. The layers between the flow channels are flipped and repeatedbetween succeeding flow channels that alternate between hydrogen andoxygen flow channels.

FIG. 12 is a flow diagram 1200 illustrating control of temperatures ofelements of the hydrogen PEM fuel cell based power generator accordingto an example embodiment. In one embodiment, the power managementcircuitry 135, also referred to as a controller, executes functions tocontrol fan speeds and hence temperature of selected elements asdescribed above.

At 1210, the controller obtains data from numerous sensors regarding thetemperature of various element and/or gas or fluid at selected portionsof the hydrogen and ambient air paths. At 1220, the signals aregenerated to control fans based on the received sensor values to controlthe temperatures of the elements to their corresponding set points. Asmentioned, the control algorithm may be based on standard PID typecontrol algorithms which may involve one or more or proportion,integral, and derivative control. If the temperature of the fuel cellstack is high, the ambient air path fan speed can be increased to helpcool the fuel cell stack. At 1230, the controller periodically repeatsmethod 1200. If programmable digital control is used, periodically meanssimple repeating the method in succession. If analog control is used,periodical may mean continuous control.

FIG. 13 is a block diagram of a specifically programmed system forexecuting control methods for a hydrogen fuel cell based power generatoraccording to an example embodiment. One embodiment of hardware andoperating environment of the system includes a general purpose computingdevice in the form of a computer 1300 (e.g., a personal computer,workstation, or server), including one or more processing units 1321, asystem memory 1322, and a system bus 1323 that operatively couplesvarious system components including the system memory 1322 to theprocessing unit 1321. There may be only one or there may be more thanone processing unit 1321, such that the processor of computer 1300comprises a single central-processing unit (CPU), or a plurality ofprocessing units, commonly referred to as a multiprocessor orparallel-processor environment. In various embodiments, computer 1300 isa conventional computer, a distributed computer, or any other type ofcomputer.

The system bus 1323 can be any of several types of bus structuresincluding a memory bus or memory controller, a peripheral bus, and alocal bus using any of a variety of bus architectures. The system memorycan also be referred to as simply the memory, and, in some embodiments,includes read-only memory (ROM) 1324 and random-access memory (RAM)1325. A basic input/output system (BIOS) program 1326, containing thebasic routines that help to transfer information between elements withinthe computer 1300, such as during start-up, may be stored in ROM 1324.The computer 1300 further includes a hard disk drive 1327 for readingfrom and writing to a hard disk, not shown, a magnetic disk drive 1328for reading from or writing to a removable magnetic disk 1329, and anoptical disk drive 1330 for reading from or writing to a removableoptical disk 1331 such as a CD ROM or other optical media.

The hard disk drive 1327, magnetic disk drive 1328, and optical diskdrive 1330 couple with a hard disk drive interface 1332, a magnetic diskdrive interface 1333, and an optical disk drive interface 1334,respectively. The drives and their associated computer-readable mediaprovide non volatile storage of computer-readable instructions, datastructures, program modules and other data for the computer 1300. Itshould be appreciated by those skilled in the art that any type ofcomputer-readable media which can store data that is accessible by acomputer, such as magnetic cassettes, flash memory cards, digital videodisks, Bernoulli cartridges, random access memories (RAMs), read onlymemories (ROMs), redundant arrays of independent disks (e.g., RAIDstorage devices) and the like, can be used in the exemplary operatingenvironment.

A plurality of program modules can be stored on the hard disk, magneticdisk 1329, optical disk 1331, ROM 1324, or RAM 1325, including anoperating system 1335, one or more application programs 1336, otherprogram modules 1337, and program data 1338. Programming forimplementing one or more processes or method described herein may beresident on any one or number of these computer-readable media.

A user may enter commands and information into computer 1300 throughinput devices such as a keyboard 1340 and pointing device 1342. Otherinput devices (not shown) can include a microphone, joystick, game pad,satellite dish, scanner, or the like. These other input devices areoften connected to the processing unit 1321 through a serial portinterface 1346 that is coupled to the system bus 1323, but can beconnected by other interfaces, such as a parallel port, game port, or auniversal serial bus (USB). A monitor 1347 or other type of displaydevice can also be connected to the system bus 1323 via an interface,such as a video adapter 1348. The monitor 1347 can display a graphicaluser interface for the user. In addition to the monitor 1347, computerstypically include other peripheral output devices (not shown), such asspeakers and printers.

The computer 1300 may operate in a networked environment using logicalconnections to one or more remote computers or servers, such as remotecomputer 1349. These logical connections are achieved by a communicationdevice coupled to or a part of the computer 1300; the invention is notlimited to a particular type of communications device. The remotecomputer 1349 can be another computer, a server, a router, a network PC,a client, a peer device or other common network node, and typicallyincludes many or all of the elements described above I/0 relative to thecomputer 1300, although only a memory storage device 1350 has beenillustrated. The logical connections depicted in FIG. 13 include a localarea network (LAN) 1351 and/or a wide area network (WAN) 1352. Suchnetworking environments are commonplace in office networks,enterprise-wide computer networks, intranets and the internet, which areall types of networks.

When used in a LAN-networking environment, the computer 1300 isconnected to the LAN 1351 through a network interface or adapter 1353,which is one type of communications device. In some embodiments, whenused in a WAN-networking environment, the computer 1300 typicallyincludes a modem 1354 (another type of communications device) or anyother type of communications device, e.g., a wireless transceiver, forestablishing communications over the wide-area network 1352, such as theinternet. The modem 1354, which may be internal or external, isconnected to the system bus 1323 via the serial port interface 1346. Ina networked environment, program modules depicted relative to thecomputer 1300 can be stored in the remote memory storage device 1350 ofremote computer, or server 1349. It is appreciated that the networkconnections shown are exemplary and other means of, and communicationsdevices for, establishing a communications link between the computersmay be used including hybrid fiber-coax connections, T1-T3 lines, DSL's,OC-3 and/or OC-12, TCP/IP, microwave, wireless application protocol, andany other electronic media through any suitable switches, routers,outlets and power lines, as the same are known and understood by one ofordinary skill in the art.

In further embodiments, power management and control electronicsincludes temperature and power output sensors that are used by thecontrol electronics to control the pump/fan speed to maintain idealtemperatures and power output. The control electronics may be configuredto maintain design points for such temperatures and power output, or mayutilize one or more equations that are parameterized based on empiricaldata obtained from operation of a nominal PEM fuel cell based powergenerator.

In one embodiment, the fuel cells charge the Li-ion battery orbatteries, which serve to provide power to a load, such as the UAS. Thebatteries provide the ability to supply higher and more dynamic levelsof power than simply utilizing the the fuel cells directly, which can beslower to respond and not normally be able to provide high levels ofcurrent that may be required for operation of the UAS in a desiredmanner, such as accelerating sufficiently while carrying a load.

EXAMPLES

1. In example 1, a fuel cell based power generator including a fuel cellelement, a water exchanger element, a hydrogen generator element, anambient air path configured to receive ambient air and provide theambient air across a cathode side of the fuel cell element, receivewater from the fuel cell element and provide wet air to the waterexchanger element, and a recirculating hydrogen air path configured toreceive hydrogen from the hydrogen generator element, provide thehydrogen past an anode side the fuel cell element to the water exchangerelement and provide wet hydrogen back to the hydrogen generator.

2. The fuel cell based power generator of example 1 and furthercomprising a rechargeable battery coupled to the fuel cell element toreceive electricity from the fuel cell element and provide electricityto a load.

3. The fuel cell based power generator of any of examples 1-2 andfurther including a fuel cell temperature sensor positioned to sense atemperature of the fuel cell element, and an ambient air path fancontroller to receive temperature information from the fuel cell elementtemperature sensor and control the ambient air path fan speed tomaintain the fuel cell element temperature at a selected temperature.

4. The fuel cell based power generator of example 3 wherein the fuelcell element selected temperature is 60° C.

5. The fuel cell based power generator of example 3 wherein the fuelcell element selected temperature is between 60° C. and 80° C.

6. The fuel cell based power generator of any of examples 1-5 andfurther including a hydrogen generator element temperature sensorpositioned to sense a temperature of the hydrogen generator element;and, a recirculating hydrogen air path fan controller to receivetemperature information from the hydrogen generator element temperaturesensor and control the recirculating hydrogen air path fan speed tomaintain the hydrogen generator element temperature at a selectedtemperature.

7. The fuel cell based power generator of example 6 wherein the hydrogengenerator element selected temperature is 80° C.

8. The fuel cell based power generator of example 6 wherein the hydrogengenerator element selected temperature is between 60° C.-100° C.

9. The fuel cell based power generator of any of examples 1-8 andfurther including a water exchanger element temperature sensorpositioned to sense a temperature of the water exchanger element, arecirculating hydrogen air path heat exchanger with fan disposed in thehydrogen air path coupled to the water exchanger element, an ambient airpath water heat exchanger element with fan disposed in the ambient airpath coupled to the water exchanger element and a fan controller toreceive temperature information from the water exchanger elementtemperature sensor and control heat exchanger fan speeds to maintain thewater exchanger element temperature at a water exchanger selectedtemperature.

10. The fuel cell based power generator of example 9 wherein the waterexchanger element selected temperature is 40° C.

11. The fuel cell based power generator of example 9 wherein the waterexchanger element selected temperature is between 40° C.-60° C.

12. The fuel cell based power generator of any of examples 1-11 whereinthe water exchanger element is coupled to receive warm wet air from theambient air path, warm dry hydrogen from the recirculating hydrogen airpath, exhaust hot dry air to ambient, and provide wet hydrogen to thehydrogen generator element via the recirculating hydrogen air path.

13. In example 13, a method includes passing ambient air via an ambientair path past a cathode side of the fuel cell to a water exchanger,picking up water from the cathode side of the fuel cell and exhaustingair and nitrogen to ambient, passing hydrogen via a recirculatinghydrogen path past an anode side the fuel cell to the water exchanger,where the water exchanger transfers water from the ambient air pathcomprising a cathode stream to the recirculating hydrogen pathcomprising an anode stream, and passing the water to a hydrogengenerator to add hydrogen to the recirculating hydrogen path and passingthe hydrogen via the recirculating hydrogen path past the anode side ofthe fuel cell.

14. The method of example 13 and further including sensing a temperatureof the fuel cell and controlling airspeed in the ambient air path tomaintain the fuel cell at a fuel cell set point temperature.

15. The method of example 14 wherein the fuel cell set point temperatureis 60° C.

16. The method of example 14 wherein the fuel cell set point temperatureis between 60° C. and 80° C.

17. The method of any of examples 13-16 and further including sensing atemperature of the hydrogen generator and controlling airspeed in therecirculating hydrogen air path to maintain the hydrogen generator at ahydrogen generator set point temperature.

18. The method of example 17 wherein the hydrogen generator set pointtemperature is 80° C.

19. The method of example 17 wherein the fuel cell set point temperatureis between 60° C. and 100° C.

20. The method of any of examples 13-19 and further including sensing atemperature of the water exchanger and controlling fans of heatexchangers in the recirculating hydrogen path and ambient air path tomaintain the water exchanger temperature at a water exchanger set pointtemperature.

21. The method of example 20 wherein the water exchanger set pointtemperature is 40° C.

22. The method of example 20 wherein the water exchanger set pointtemperature is between 40° C. and 60° C. Although a few embodiments havebeen described in detail above, other modifications are possible. Forexample, the logic flows depicted in the figures do not require theparticular order shown, or sequential order, to achieve desirableresults. Other steps may be provided, or steps may be eliminated, fromthe described flows, and other components may be added to, or removedfrom, the described systems. Other embodiments may be within the scopeof the following claims.

1. A method comprising: passing ambient air via an ambient air path pasta cathode side of the fuel cell to a water exchanger; picking up waterfrom the cathode side of the fuel cell and exhausting air and nitrogento ambient; passing hydrogen via a recirculating hydrogen path past ananode side the fuel cell to the water exchanger, where the waterexchanger transfers water from the ambient air path comprising a cathodestream to the recirculating hydrogen path comprising an anode stream;passing the water to a hydrogen generator to add hydrogen to therecirculating hydrogen path, the hydrogen generator directly connectedto the water exchanger; and passing the hydrogen via fan in therecirculating hydrogen path past the anode side of the fuel cell, thefan disposed in the recirculating hydrogen path after the hydrogengenerator and before the fuel cell.
 2. The method of claim 1 and furthercomprising: sensing a temperature of the fuel cell; and controllingairspeed in the ambient air path to maintain the fuel cell at a fuelcell set point temperature.
 3. The method of claim 2 wherein the fuelcell set point temperature is 60° C.
 4. The method of claim 2 whereinthe fuel cell set point temperature is between 60° C. and 80° C.
 5. Themethod of claim 1 and further comprising: sensing a temperature of thehydrogen generator; and controlling airspeed in the recirculatinghydrogen air path to maintain the hydrogen generator at a hydrogengenerator set point temperature.
 6. The method of claim 5 wherein thehydrogen generator set point temperature is 80° C.
 7. The method ofclaim 5 wherein the fuel cell set point temperature is between 60° C.and 80° C.
 8. The method of claim 1 and further comprising: sensing atemperature of the water exchanger; and controlling fans of heatexchangers in the recirculating hydrogen path and ambient air path tomaintain the water exchanger temperature at a water exchanger set pointtemperature.
 9. The method of claim 8 wherein the water exchanger setpoint temperature is 40° C.
 10. The method of claim 8 wherein the waterexchanger set point temperature is between 40° C. and 60° C.